Neon lamp warning circuit



March 26, 1968 A. F. HOUGHTON 3,375,402

NEON LAMP WARNING CIRCUIT Filed April 16, 1965 FIGQI s 7 FIG. 4 l2 FIG. 5

INVENTOR 60v ALAN FQISHER HOUGHTON ATTORNEY United States Patent 3,375,402 NEON LAMP WARNING CIRCUIT Alan F. Houghton, Dunedin, Fla., assignor to General Electric Company, a corporation of New York Filed Apr. 16, 1965, Ser. No. 448,798 4 Claims. (Cl. 315-176) ABSTRACT OF THE DISCLOSURE A neon lamp indicates energization of a high D.C. voltage source. A separate power supply, including an alternating current source and a zener diode, supplies a pulsating voltage to the neon lamp of a value above that needed to sustain ionization but slightly below that needed to initiate ionization so that when the high DC. voltage is energized, the addition of a small pre-ionizing voltage developed from the high DC. voltage source ionizes the lamp. In alternate embodiments, either positive or negative senses of the high DC. voltage source can be indicated.

This invention relates to a neon lamp high voltage warning circuit and more specifically to a warning circuit in which the neon lamp provides a constant, high intensity indication over a wide range of high D.C. voltages while drawing very little current from the high voltage supply.

Neon lamps have commonly been used in voltage indicating circuits with one of the particular uses being to provide an indication and a warning of the presence of a high voltage DC. at a particular terminal. In warning circuits of this type, two particular difficulties are encountered which detract from the reliability and eificiency of the circuit. The first of these difficulties was that due to the inherent nature of neon lamps, varying voltages applied to the lamp would cause the lamp to ionize with varying intensities. Quite often this would lead to false indications followed by costly damage to electronic equipment. The second problem encountered in prior neon lamp high voltage indicating circuits was that the lamps themselves drew a considerable amount of current from the high voltage source. In situations where the power sup ply was of the high voltage, low current type, this overload of the power supply caused gross ineificiencies.

It is an object of the present invention to provide an improved neon lamp high voltage warning circuit.

It is another object of this invention to provide a neon lamp warning circuit which produces a constant, high intensity output for varying power supply voltages.

It is a further object of this invention to provide a neon lamp Warning circuit which provides a high voltage indication while drawing very little current from the power supply.

Briefly, these objects are met in a warning circuit which employs a separate alternating current power supply to provide the major part of the current necessary to ionize the neon lamp. Very little current from the high voltage power supply will thus be needed to completely ionize the neon lamp to its full intensity and this little current can be provided from a wide range of supply voltages.

The novel features of this invention are set forth with particularity in the appended claims. However, the invention may be better understood as to its organization and scope by referring to the following specifications and drawings, to which:

FIGURE 1 is a schematic diagram of one embodiment of this invention which is designed to indicate and if necessary provide a warning of positive high voltages;

FIGURE 2 is another embodiment designed to indicate negative high voltages;

FIGURE 3 is a further embodiment designed to provide an indication for both positive and negative high voltages; and

FIGURE 4 is another embodiment designed to provide high voltage indication at a plurality of terminals;

FIGURE 5 is a voltage wave form at one of the electrodes of the neon lamps in the circuits of FIGURES 1, 2, 3, and 4.

Referring now to FIGURE 1, there is illustrated a DC. high voltage terminal 1 at which high voltages of varying magnitudes may or may not be present. A current limiting resistor 2 is connected from terminal 1 to electrode 3 of a neonlamp 4. The neon lamp 4 is a typical neon lamp in that the voltage necessary to ignite or completely ionize the lamp is higher than the voltage necessary to sustain ignition of the lamp once it has been started. One side of an A.C. voltage source, which is relatively low in magnitude compared with the high D.C.

. voltage at terminal 1, is connected to the electrode 3 of the lamp. When a high voltage lamp 4 through a resistor 5 and diodes 6 and 7. A zener diode 8 is connected between electrode 9 of lamp 4 and of the junction of diodes 6 and 7. The other side of the A.C. lamp supply voltage is connected to electrode 9 of the neon lamp 4.

In the operation of the embodiment of FIGURE 1, the current from the A.C. lamp supply is limited by resistor 5 to a reasonable value and the negative cycles of the A.C. voltage are blocked by the diode 6. It is possible to obtain similar results by eliminating diode 6 and substituting for resistor 5 another resistor with a value of resistance much higher than that needed when the diode is used. Zener diode 8 clips the rectified voltage at a value lying somewhere'between the sustaining voltage and the ignition voltage of the neon lamp 4. Diode 7 blocks the current flowing from the high voltage source at terminal 1 from the zener diode 8. When there is no voltage present at terminal 1, the zener voltage from the A.C. lamp supply at electrode 3 of lamp 4 is not sufiicient to ignite is present at terminal 1, a small amount of current is allowed to flow through limiting:resistor 2 to pre-ionize the lamp. When the lamp is pre-ionized, the zener voltage pulses provide the additional current necessary for the lamps constant high output of light. Thus, the relatively small amount of current from the high voltage at terminal 1 ger the lamp into a highly ionized state.

The positive zener pulses from the A.C. voltage source supply power to the lamp and cause it to glow brightly with a constant intensity. Ionization of the lamp will con-. tinue so long as the pre-ionizing trigger current from the high voltage at terminal 1 is supplied. When this high voltage is removed from terminal 1, the lamp is not preionized between pulses and, therefore, the lamp cannot ignite.

is sufiicient to trig- In. a. Working embodiment the following circuit parameter values and types were used:

.A.C. source 117 v.

Resistor 2 100 megohms. Resistor 5 100 ohms. .Diode 6 1N93.

Diode 7 1N93.

Zener diode 8 60 v. 1N1369. Neon lamp 4 NE2.

High voltage range 250 v.-10,000 v.

A 22K ohm resistor may be substituted therefor.

In the embodiment of FIGURE 2, a negative DC. voltage can be indicated by connecting terminal 1 to electrode 9 of lamp 4 through resistor 2. In this embodiment the blocking diode 7 is reversed but in all other aspects the circuit is similar to the circuit of FIGURE 1. In the operation of FIGURE 2 the diode 7 blocks the negative voltage from the zener diode and the large limiting resistor 2 allows only a few microamperes of current to flow to the electrode 9 of the neon lamp 4. This small current creates a negative pre-ionizing voltage at electrode 9 which effectively adds to the zener voltage at electrode 3 causing the lamp to ionize.

With the addition of a second blocking diode 10 and a second limiting resistor 11, as illustrated in FIGURE 3, the presence of either a positive or negative DC. voltage at terminal 1 can be indicated. If a positive high voltage is present at terminal 1, a positive pre-ionizing voltage adds to the zener voltage at electrode 3 and causes the lamp to ionize. If, on the other hand, a negative voltage is present at terminal 1, a negative pre-ionizing voltage is developed at electrode 9 of lamp 4 which efiectively adds to the positive zener voltage at electrode 3. In this manner negative voltages are indicated by ionization of the lamp. Blocking diode 7 blocks positive high voltages from the anode of the zener diode and diode 11 blocks negative high voltages from the cathode of the zener diode.

FIGURE 4 illustrates how more than one indicating lamp, and therefore more than one source of high voltage, can be served from only one source of AC. voltage and one zener diode. Resistor 12 is shown in place of resistor 5 and diode 6 between the source of AC. voltage and the zener diode 8. The zener voltage pulses provide current to the neon lamps 4a, 4b, and 40 through diodes 7a and 10a, 7b, and 70 respectively. Limiting resistors 13a, 13b, and 13c, in series with diodes 7a, 7b, and 7c respectively, insure ignition of all lamps. A typical value for resistors 13a, b and c may be 5K ohms.

A high positive or negative voltage terminal 1a is monitored by lamp 4a in the same manner as the circuit of FIGURE 3. A high negative voltage terminal 1b and a high positive voltage terminal 1c are monitored by lamps 4b and 40 respectively. The operations of the latter circuits are similar tothose of FIGURES 2 and 1 respectively.

As indicated above, FIGURE 5 illustrates the voltage wave form present at the electrode 3 of neon lamp 4. The negative cycles of the AC. source are blocked by diode 6. The zener diode clips the positive cycles at a level just below the ionizing voltage of the lamp so that the resulting voltage at electrode 3 has the flat top wave form illustrated in FIGURE 4.

The'major part of the ionizing voltage is typically supplied from a 60 cycle A.C. supply voltage and only a small amount of pre-ionizing current, in the microampere range, is needed from the high voltage source. Since very little current is required from the high voltage source, the efficiency of the circuit is quite high. Additionally, since the current from the high voltage source is utilized only as a trigger for a pre-ionizing current, its particular value is not critical and the reliability of the circuit may be maintained over a wide range of high voltage magnitudes.

Although, I have described my invention in a particular embodiment, the principle underlying the invention will suggest many modifications of this embodiment to those skilled in the art. Therefore it is desired that the appended claims not be limited to the described embodiment but rather should encompass all such modifications as fall within the spirit and scope of this invention.

What is claimed as new and desired to secure by Letters Patent of the United States is:

1. In a neon lamp indicating circuit including a neon lamp the ionization of which indicates the presence of high DC. voltage, the improvement comprising a pulsating source of supply voltage, clipping means connected across said supply voltage source to limit the peaks to a magnitude slightly below the ionizing potential of said neon lamp, means connecting said supply voltage source across said neon lamp, means for developing a second voltage from the high DC voltage of such magnitude that the sum of the second voltage and the peak magnitude of the pulsating supply voltage is sufficient to cause ionization of said neon lamp, means connecting said second voltage develo in means to said neon lamp, and said supply voltage connecting means including unidirectional blocking means blocking the second voltage from said pulsating voltage source. I

2. An indicating circuit for determining the presence of high DC. voltage at a terminal, comprising a neon lamp including a first and a second electrode; a hunting resistor connecting said terminal to said first elec-- trode and being sutficiently large so as to present only a pre-ionizing voltage at said first electrode when high voltage is present at the terminal; a source of pulsating voltage, the polarity of the pulses being the same as the polarity of the pre-ionizing voltage; a diode connecting a first side of said source of pulsating voltage to said first electrode and being poled to allow current fiow from said source of pulsating voltage to said first electrode; a zener diode connected from the common junction of said diode and the first side of said source of pulsating voltage to a second side of said source and functioning to ltm1t the pulsating voltage to a value slightly below the iomzing voltage of said neon lamp but being sufficiently large such that when the pulsating voltage is added to the prc ionizing voltage at said first electrode the lamp will ionize, and means connecting the second side of said source to said second electrode.

3. An indicating circuit for determining the presence of a high DC. voltage at a terminal, comprising a neon lamp including a first and a second electrode; a limitingresistor connecting said terminal to said second elec trode; a limiting resistor connecting said terminal to said second electrode and being sufiiciently large so as to apply only a pre-ionizing voltage at said second electrode when high voltage is present at said terminal; a source of pulsating voltage, the polarity of the pulses being of a polarity opposite to that of the pre-ionizing voltage and means connecting a first side of said source to said first electrode; a diode connecting a second side of said source of pulsating voltage to said second electrode and being poled to allow current flow from said second electrode to said source of pulsating voltage; a zener diode connected across said source of pulsating voltage to limit the pulsating voltage to a value slightly below the ionizing voltage of said neon lamp but being sufiiciently large such that when the pulsating voltage is effectively added to the pre-ionizing voltage at said second electrode the lamp will ionize.

4. An indicating circuit for determining the presence of high negative or positive DC. voltage at a terminal, comprising a neon lamp including a first and a second electrode; first and second limiting resistors respectively connecting said terminal with said first and second electrodes and being sufiiciently large so as to apply only a pre-ionizing voltage to said first and second elecs trodes when high positive or negative voltage is present,

5 at said terminal; a source of pulsating voltage, the polarity of the pulses being the same as the polarity of the pre-ionizing voltage applied to said first electrode and being of a polarity opposite to that of the pre-ionizing voltage applied to said second electrode; a zener diode including an anode and cathode electrodes connected across said source of pulsating voltage to limit the pulsating voltage to a value slightly below the ionizing voltage of said neon lamp but being sufliciently large such that when the pulsating voltage is added to the pre-ionizing voltage at said first or second electrodes the lamp Will ionize, a first diode connected from said anode of said zener diode to said first electrode to block high voltages at said terminal from said anode, and a second diode connected from said cathode of said zener diode to said second electrode to block high voltages at said terminal from said cathode.

References Cited UNITED STATES PATENTS 2,411,848 12/1946 Cami-as 315-176 2,848,685 8/1958 Mondschein 315-176 2,920,239 1/1960 Saeger 31S176 10 3,060,326 10/1962 Watson 30788.5

JOHN W. HUCKERT, Primary Examiner. I. D. CRAIG, Assistant Examiner. 

